In answer to your question, you should not have any problem with your AT&T cell phone service if your plan includes being able to call in North America.
What happened to me was that I purchased my plan from AT&T in Mexico and when I arrived in the US, I was unable to call anyone. I was able to use WhatsApp. My thinking at the time was that since my contract is with AT&T, that I could simply go into a branch and get help. They had no record of my plan as the company is not associated, so they would or could not help me.
Interestingly, I just purchased a new cell phone in the US, and with the same Sims and number from the old phone, everything works. It is a mystery.